1. Field of the Invention
The present invention relates to a hydraulic power steering apparatus used in a vehicle, and more particularly to a hydraulic power steering apparatus provided with a check valve regulating a back flow of a working fluid from a hydraulic actuator generating a steering assist force to a hydraulic pump side.
2. Description of the Related Art
In a hydraulic power steering apparatus provided with a hydraulic actuator generating a steering assist force, in order to prevent a phenomenon (a so-called kickback phenomenon) that a working fluid supplied to the hydraulic actuator flows back to a hydraulic pump side and a steering wheel is moved based on an external force applied to a tire wheel at a time when a vehicle runs on a curb or the like, there is a case that a check valve inhibiting the back flow of the working fluid is provided. Further, in the check valve mentioned above, there has been known a structure in which a valve element slidably accommodated within a valve body has a plate-like guide portion which is surface contacted with an inner peripheral surface of the valve body (refer, for example, to Japanese Patent Application Laid-open No. 2003-165454 (patent document 1)).
In this case, in the structure in which the valve element has the plate-like guide portion which is surface contacted with the inner peripheral surface of the valve body, since a width in a peripheral direction of the guide portion is approximately uniform all over the guide in a diametrical direction including a slidable contact surface of the guide portion brought into slidable contact with the inner peripheral surface, the valve element is hardly inclined with respect to a center axis of the valve body based on a flow of the working fluid. In order to move in parallel to the center axis, it is necessary to increase a number of the guide portion while suppressing an increase of the sliding resistance. However, if the number of the guide portion is increased, the width in the peripheral direction of a valve internal oil path formed by a pair of guide portions adjacent to each other in the peripheral direction becomes small, and a flow path resistance becomes large.